The present invention to device adapted to be coupled to means presenting a service of which the price can be calculated as a function of a predetermined number of unitary taxes depending each in a known manner on the value of a basic tax, said means being adapted to transmit to said device data corresponding to the appearance of the various unitary taxes, said device comprising a pulse receiving circuit detecting said data, a logic adaptor circuit connected to said receiving circuit, a computing interface circuit responsive to said logic adaptor circuit and adapted, as new taxes accumulate in the device, to deliver a signal corresponding to the price of each unitary tax, and adder circuit coupled to the output of said computing interface circuit for adding the prices of the various unitary taxes accumulated since the last resetting of the device, and a first announcing member displaying said sum corresponding to the price to be paid for the service rendered.
The user of a public or private service, for example the subscriber of a telephone line connected to a telephone exchange, may allow a third person, referred to hereinafter as "a temporary user", to take advantage of this service against the payment of a predetermined sum.
This sum depends in general on a function f (n, t, . . .) of several variables (n, t . . .) known to the user, at least when the service has been utilized. In the above example and assuming that the telephone line is designed for retransmitting counting pulses, the sum to be paid by the temporary user depends on the value of a basic tax and also on the number n of unitary call charges t.sub.j (j = 1 to n) applied during the call or calls made by this temporary user, each unitary call charge depending in a known manner on the value of the basic tax t.
At present devices are known which permit of displaying the number n of unitary taxes or call charges to be entered into the subscriber's account. However, it is not sufficient to know this number n for determining directly the value of the sum to be paid to the user, for the relationship f (n, t . . .) may be relatively complex and evolve periodically. It is therefore necessary to use tables the existence of which if generally unknown to, and beyond the control of, the temporary users; in other words, present conditions facilitates both frauds and misuses.